Rapid assembly casting system for slab gels

ABSTRACT

Flat plates serving as molds and enclosures for slab gels are held together by a clamping frame in which the side edges of the plates slide into facing channels and are clamped by lever-operated cams that compress the channel walls against the plate surfaces. The joined plates are held on a vertical support rack containing a finger-operated spring-loaded notched clamp that presses down on the plates to seal the opening at the bottom edges of the plates against a gasket. A well-forming comb for insertion between the plates contains flexible outwardly angled fingers to seal against the spacers between the plates.

[0001] This invention lies in the field of electrophoresis inslab-shaped gels, and particularly in the methods and types of apparatusused for casting slab-shaped gels from a liquid gel-forming solution.

BACKGROUND OF THE INVENTION

[0002] Electrophoresis in slab gels is widely used for separating andanalyzing mixtures of chemical species, and particularly mixtures ofcomplex species such as proteins, polypeptides, nucleic acids andoligonucleotides. Slab gels permit the simultaneous analysis of multiplesamples as well as the inclusion of standards to facilitate theidentification of the species. Once the separation has been performed, aslab gel is easily removed from its enclosure and readily stained fordetection and analysis.

[0003] Electrophoresis gels are prepared by polymerization of monomersin liquid solutions. Some of the largest sources of operator error andloss of time in the laboratory with slab gel electrophoresis are in thepreparation stages of the gel and particularly in the casting procedure.With many types of apparatus, it often difficult to achieve properalignment and assembly of the parts in a leak-proof manner withoutdamage or breakage. The procedure requires time-consuming care,particularly when performed by those who are inexperienced. The presentinvention seeks to address these difficulties.

SUMMARY OF THE INVENTION

[0004] This invention resides in several novel aspects of the structureand use of casting systems for slab gels. The various aspects areindependently useful and can be included individually in gel castingsystems or in combination.

[0005] One aspect of this invention is a cam-operated mounting frame forholding flat plates and spacers together in a fluid-tight enclosure. Theside edges of the stacked glass plates (including spacers, which may bebonded to one of the plates or separate strips for insertion between theplates) slide into a pair of facing channels in a loose fit, and thewalls of the channels are compressible against the plates bylever-operated cams that hold the plates and spacers against one anotherin a fluid-tight manner. Another aspect of the invention addresses themanner in which the joined plates are secured to a vertical support rackwhere gel-forming solution is placed in the gap between the plates andallowed to solidify and form the gel. In this aspect, the joined platesare held on a vertical support rack with the bottom opening of theplates pressed against the floor of the rack by a spring-loaded notchedclamp at the top of the rack, the clamp being one that is readily openedand closed by a finger tab. A third aspect of the invention resides in avariation on the commonly used inserts or “combs” that are placed in thegel space to form sample wells in the gel as the gel is being cast.Flexible fingers at each end of the row of teeth (the well-formingprotrusions on the insert) serve to seal the insert against the spacersto reduce the risk of leakage of liquid around the insert.

[0006] These and other aspects, features, objects, and advantages of theinvention will become more evident from the description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a perspective view, partially exploded, of a gel castingstand embodying features of the present invention.

[0008]FIG. 2 is a front elevation view of a clamping frame for a gelplate assembly in accordance with this invention, identical to thatshown mounted to the casting stand in FIG. 1.

[0009]FIG. 3 is a cross section of the clamping frame and gel plateassembly of FIG. 2, taken along the line 3-3 of FIG. 2.

[0010]FIG. 4 is a side view of a notched clamp in accordance with thisinvention, the clamp being one of the components shown in theperspective view of FIG. 1.

[0011]FIG. 5a depicts a well-forming insert or “comb” in accordance withthis invention. FIG. 5b shows the insert positioned between the spacersof a gel plate assembly.

DETAILED DESCRIPTION OF THE INVENTION AND SPECIFIC EMBODIMENTS

[0012] In each of its several aspects, this invention can be implementedin a wide range of embodiments differing in structure, shape, and mannerof operation. For a better understanding of the features that are commonto these various embodiments, however, the following description willfocus on the specific examples that are shown in the drawings. These areonly illustrative, however.

[0013] The perspective view in FIG. 1 is that of a slab gel castingsystem that incorporates several aspects of the invention, illustratinghow various features and parts fit together and coact. The system ofFIG. 1 is designed for the casting of two slab gels independently on asingle support rack 11 with left and right mounting stations 12, 13 in aside-by-side arrangement. The left mounting station 12 is shown empty,i.e., without a gel plate assembly, and with certain parts separatedfrom the support rack to more clearly show the structure of the rack.The separated parts are the pivoting notched clamp 14, a pin 15 tosecure the notched clamp to the support rack, and a coil spring 16 tobias the notched clamp, all of which are described in more detail below.

[0014] The gel enclosures to be used in the gel casting system of thisand the succeeding drawings are any of the wide variety of gel plateassemblies used in slab electrophoresis, generally consisting of twoflat rectangular plates separated by spacers between the plates alongthe opposing side edges of the plates, the spacers defining both thethickness of the gel due to their own thickness and the width of the geldue to the distance between the spacers. The spacers may be bonded to ormolded as part of the surface of one of the two plates or separatestrips of spacing material inserted between the flat plates. Anillustrative gel plate assembly of this type is more visible insucceeding drawings and is further described in the descriptions ofthose drawings.

[0015] Components made visible on the left mounting station 12 include afloor 21 to support the bottom edge of the gel enclosure, a flatrectangular gasket 22 resting on the floor, and a vertical wall 23against which the back of the gel enclosure rests. Extending upward fromthe top of the vertical wall are a pair of brackets 24 for mounting thenotched clamp 14 to the support rack. Mounting is achieved by the pin 15which passes through holes 25 in the brackets and a hole 26 in thenotched clamp.

[0016] The right mounting station 13 is identical to the left mountingstation 12 and is shown with the notched clamp 14 installed, togetherwith a gel plate assembly 31 which includes a pair of flat rectangularglass plates 32, 33 of unequal height, the rear plate 32 having an upperedge extending above the upper edge of the forward plate 33. The twovertical side edges of the rear plate are slightly thicker than thecentral portion of the plate, forming raised platforms to serve asspacers for the forward plate, leaving a gap between the two plates forcasting the gel. The gel plate assembly 31 also includes a clampingframe 34 that secures the two plates together to form fluid-tightclosures along their side edges. The upper edge of the rear plate 32 isengaged by the notched clamp 14, which presses the rear plate and hencethe entire gel plate assembly downward against the gasket to form afluid-tight closure. The bottom and sides of the gel plate assembly arethus closed off, and a gel-forming solution can be poured into the spacebetween the glass plates through the opening at the top between the twoplates of unequal height.

[0017] A feature included in the support rack for added convenience is arow of holes 38 for holding tubes for samples or reagents. This makesthe casting system a compact unit that serves multiple functions.

[0018] Detailed views of the gel plate assembly and clamping frame areseen in the front elevation view of these components in FIG. 2 and thecross section view of FIG. 3. The two glass plates 32, 33 are visible inboth drawings. The spacers are shown in FIG. 2 as raised platforms 35integrated into the structure of the rear plate 32 along the two sideedges of the plate. FIG. 3 shows the spacers as separate strips 36. Ineither case, the spacers define a gap 37, visible in FIG. 3, to serve asthe gel space. The clamping frame is a four-sided rectangular frame 41open at the center, with retaining members 42, 43 (FIG. 3) along each ofthe two side edges. The retaining members have C-shaped profiles whoseconcave sides (referred to herein as channels or grooves 44, 45) facetoward the center of the frame and each other. The grooves are largeenough to loosely receive the side edges of the two glass plates with aspacer in between, and glass plates and spacers can thus be insertedinto the retaining members from one end and slid along the lengths ofthe grooves until fully inserted. The length of each retaining member ispreferably more than half the length of the side edge (i e., the height)of the shorter glass plate.

[0019] The outer walls 46, 47 of the retaining members are bendable andresilient. The wall 47 shown on the right side of FIG. 3 is in a relaxedcondition, leaving the groove wide enough to allow free movement of theglass plates and spacer within the groove, while the wall 46 on the leftside of the drawing is bent or distorted inward to contact the forwardglass plate 33 and press the plates and spacer against each other. Theinward bending and relaxation of the two bendable walls are controlledby the positions of two lever-operated cams 51, 52, each mounted to theframe in a rotatable manner by pins 53, 54 (shown in dashed lines). Thelever 55 on the left cam is shown in a lowered position in which the camitself 57 engages the bendable wall 46 pressing the wall against theglass plates. The lever 56 on the right cam has been rotated to a raisedposition, rotating the cam 58 out of contact with the bendable wall 47and thereby releasing the wall from the glass plates. Each campreferably extends substantially the full length of the correspondingbendable wall.

[0020]FIG. 4 offers an enlarged view of the notched clamp 14 and itsoperation. The clamp, represented in solid lines, is in engagement withthe upper edge 61 of the rear glass plate 32, the corner of the upperedge fitting within the notch 62 in the clamp which presses the glassplates downward against the gasket 22 (shown in FIG. 1). When the clampis rotated around the mounting pin 15 to the position shown in dashedlines, the pressure is released. The spring 16 biases the clamp towardthe clamping position (solid lines). Manual operation of the clamp isfacilitated by the finger tab 63. This tab, in conjunction with thestationary finger tab 64 (FIG. 1) on the support rack permits easyengagement and release of the notched clamp 14 by simply squeezing thetabs together (and thereby compressing the coil spring 16) to open theclamp and releasing them to close the clamp and engage the gel plateassembly.

[0021] An additional feature or aspect of the present invention is aself-sealing insert for forming sample wells in the gel as the gel isbeing cast. Well-forming inserts are commonly referred to in patents andother literature as “templates” or “combs,” the latter term reflectingthe comb-like shape of the insert due to the teeth-like projections orprotrusions that define the number, spacing and shape of the wells. Theinsert fits inside the gap between the glass plates and is placed alongthe upper edge of the gap with the teeth extending into the gelsolution. When the gel sets, the insert is removed and the voids left bythe teeth serve as wells for the placement of liquid samples to beseparated by the electrophoretic analysis. The teeth may be of any shapebut at most often rectangular and regularly spaced. Typical teeth are ofthe dimensions 0.20 inch (0.51 cm)×0.40 inch (1.02 cm), spaced apart bya distance of 0.11 inch (0.28 cm).

[0022] An illustration of an insert incorporating the novel features ofthe present invention appears in FIGS. 5a and 5 b. FIG. 5a shows theinsert entirely separate from the gel plate assembly. The insertconsists of a flat strip 66 of solid, substantially rigid material witha row of teeth 67 of identical shape and equal spacing, extendingperpendicularly from one side of the strip. While the insert shown inthe drawing contains eight teeth, the number of teeth is not criticaland inserts with different numbers of teeth (such as five, nine, ten, orfifteen) can be used as well. At the two extremities of the row areoutwardly angled protrusions or fingers 68, 69. Each of theseprotrusions is flexible and resiliently bendable inward toward theremaining teeth. When the insert is placed between the glass plates andbetween the spacers 36, as shown in FIG. 5b, the end fingers 68, 69 aredistorted from their relaxed condition and press against the inner edgesof the spacers 36 to hold the insert in place and to form a lateralseal. Gel-forming solution that is placed in the gap between the glassplates is thus prevented from spillage around the ends of the insert bycapillary action or when the gel plate assembly is lifted or handled.

[0023] Once the gel is cast, the plates and spacers with the gel inbetween can be removed from the support rack and from the clampingframe, and are then readily transferred to any electrophoresis cellappropriately sized to accept the assembled plates. One example of suchas cell is the “Mini-PROTEAN® 3” Mini Vertical Electrophoresis System, aproduct of, and commercially available from, Bio-Rad Laboratories, Inc.,of Hercules, Calif., USA. A description of this type of cell is found inU.S. Pat. No. 5,632,877 (“Rapid Assembly Electrophoresis Cell for SlabGels,” D. L. Van Atta, inventor, issued May 27, 1997).

[0024] The foregoing is offered primarily for purposes of illustration.It will be readily apparent to those skilled in the art that theconfigurations, relative dimensions, operating procedures and otherparameters of this invention can be further modified or substituted invarious ways without departing from the spirit and scope of theinvention.

What is claimed is:
 1. Apparatus for securing together a plate andspacer assembly comprising a pair of flat plates with spacers in betweento serve as a mold for casting an electrophoresis slab gel, saidapparatus comprising: a frame having two parallel edges, each such edgehaving an inward-facing groove formed therein, said grooves positionedto loosely receive opposing edges of said plate and spacer assembly;each said groove bordered by a wall that is resiliently bendable to varythe width of said groove; and cam means pivotally mounted to said frameto engage said resiliently bendable walls, said cam means capable ofmanual rotation between (i) a clamping position in which said cam meansurge said resiliently bendable walls into said grooves, therebynarrowing the widths of said grooves and clamping a plate and spacerassembly into said frame, and (ii) an open position in which said cammeans release said bendable walls, thereby permitting insertion andremoval of said plate and spacer assembly.
 2. Apparatus in accordancewith claim 1 in which said cam means comprise first and secondindependently operable cams, one engaging each of said resilientlybendable walls.
 3. Apparatus in accordance with claim 1 in which saidcam means comprise first and second cams, one engaging each of, andextending substantially the full length of, said resiliently bendablewalls.
 4. A combination of (i) a plate and spacer assembly and (ii) anapparatus for securing said plate and spacer assembly together to serveas a mold for casting an electrophoresis slab gel, said combinationcomprising: a plate and spacer assembly comprising a pair of flat plateswith spacers in between; a frame having two parallel edges, each suchedge having an inward-facing groove formed therein, said groovespositioned to loosely receive opposing edges of said flat plates withsaid spacers therebetween; each said groove bordered by a wall that isresiliently bendable to vary the width of said groove; and cam meanspivotally mounted to said frame to engage said resiliently bendablewalls, said cam means capable of manual rotation between (i) a clampingposition in which said cam means urge said resiliently bendable wallsinto said grooves, thereby narrowing the widths of said grooves andclamping said plate and spacer assembly into said frame, and (ii) anopen position in which said cam means release said bendable walls,thereby permitting insertion and removal of said plate and spacerassembly.
 5. Apparatus in accordance with claim 4 in which said cammeans comprise first and second independently operable cams, oneengaging each of said resiliently bendable walls.
 6. Apparatus inaccordance with claim 4 in which said cam means comprises first andsecond cams, one engaging each of, and extending substantially the fulllength of, said resiliently bendable walls.
 7. A casting stand forholding a rectangular slab gel enclosure having a bottom opening andsecuring said enclosure in a vertical position for casting a gel in saidenclosure, said casting stand comprising: a support rack having a floorsized to cover said bottom opening and a vertical wall extending upwardfrom said floor; a notched member pivotally mounted to said support rackabove said floor, said notched member having a notch therein to receivean upper edge of said enclosure when said enclosure is resting againstsaid vertical wall, said notched member capable of rotation between aclamping position in which said enclosure is received within said notchwhen said bottom opening is pressed against said floor, and an openposition in which said notch is raised to release said enclosure frompressure against said floor and to thereby permit insertion and removalof said enclosure from said support rack, said notched member beingspring-loaded to bias said notched member toward said clamping position.8. A casting stand in accordance with claim 7 further comprising agasket sized to cover said floor.
 9. A casting stand in accordance withclaim 7 in which said notched member comprises a tab accessible formanual manipulation to rotate said notched member between said clampingposition and said open position.
 10. A casting stand in accordance withclaim 7 in which said tab is defined as a movable tab, and said castingstand further comprises a stationary tab extending from said supportrack at a location adjacent to where said notched member is pivotallymounted to said support rack, said stationary and movable tabs arrangedsuch that manually pressing said movable tab against said stationary tabwill cause said notched member to be drawn from said clamping positionto said open position while release of said movable tab will return saidnotched member into said clamping position.
 11. An insert for placementin a slab gel mold to form wells in a slab gel cast in said mold, saidinsert comprising: a flat strip of solid, substantially rigid materialwith a series of regularly spaced protrusions extending from an elongateedge of said strip perpendicularly to said edge; and two end protrusionsextending from said strip, one at each end of said series of regularlyspaced protrusions, said end protrusions angled outward away from saidregularly spaced protrusions, said end protrusions being resilientlybendable inward toward said regularly spaced protrusions.
 12. Apparatusfor casting an electrophoresis slab gel with sample wells along one edgeof said gel, said apparatus comprising: (a) a plate and spacer assemblycomprising a pair of flat plates separated by a pair spacers, onelocated along each of two opposing edges of said plates; and (b) aninsert for forming said wells, said insert comprising (i) a flat stripof solid, substantially rigid material sized for insertion between saidplates, (ii) a series of regularly spaced protrusions extending from anelongate edge of said strip perpendicularly to said edge, and (iii) twoend protrusions extending from said strip, one at each end of saidseries of regularly spaced protrusions, said end protrusions angledoutward away from said regularly spaced protrusions, the distancebetween the outer extremities of said end protrusions being wide thanthe distance between said spacers, said end protrusions beingresiliently bendable inward to form a fluid-tight seal against saidspacers.